How to use the router level dependency in the routes? #8810

abbazs · 2021-08-27T13:26:38Z

abbazs
Aug 27, 2021

Example Code

def get_db_connection():
    conn = pymssql.connect(
        server=settings.server,
        user=settings.user,
        password=settings.password,
        database=settings.database,
        port=settings.port,
        as_dict=True,
    )
    try:
        yield conn
    finally:
        conn.close()


router = APIRouter(
    prefix="/project",
    tags=["project"],
    dependencies=[Depends(get_db_connection)],
    responses={418: {"description": "Project status API."}},
)


@router.get("/count/{status}")
def projects_count(
    status: str, conn: pymssql.Connection = Depends(get_db_connection)
) -> dict:
    try:
        if status.upper() == "ALL":
            status = None
        return aq.get_project_count(conn, status=status)
    except:
        raise HTTPException(404, "Unable to get project count")

Description

There are several endpoints in the router. And all of them have the parameter conn. Can I avoid declaring this parameter at each router by declaring it as the dependency at APIRouter? And how to access the dependency declared at APIRouter in a route?

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.66.0

Python Version

3.9.6

Additional Context

When I did google search for the same, the following is what I get:
#424
https://stackoverflow.com/questions/63961339/how-to-access-route-dependencies-in-custom-apiroute-class
https://stackoverflow.com/questions/64506036/fastapi-how-to-access-attributes-of-class-based-dependency-inside-route-when-dep

Is there a simpler solution?

Answered by arielnmz

Aug 3, 2024

Re:

I don't see how this solves anything.

I think the solution looks like this:

router = APIRouter(prefix="/items", tags=["items"])

DBSession = Annotated[Session, Depends(get_db)]

@router.get("/")
async def customers_list(db: DBSession) -> list[Item]:
    return db.do_something()

Two things:

Notice how I skipped dependencies=[Depends(get_db)] from APIRouter and instead declared annotated Session with the dep.
Notice how you don't have to do db: Session = Depends(get_db) on every route handler.

Imo seems counter intuitive, but I think the magic was that Session being Annotated makes FastAPI inject it to the route handler.

View full answer

jiteshy · 2021-08-31T19:08:02Z

jiteshy
Aug 31, 2021

The way you have specified dependencies in APIRouter as below is correct (Reference: Dependency in APIRouter ) :
dependencies=[Depends(get_db_connection)]

This can be taken even one more level up to declaring FastAPI app if it's needed for all the Routers (Reference: Dependency in FastAPI )
app = FastAPI(dependencies=[Depends(get_db_connection)])

With that, I think accessing the dependency as below should work considering you are specifying the dependency in the router (It worked for my sample code).

router.dependencies[0].dependency()

however I am not sure if there is a more elegant way to access the Router/App level dependencies in endpoints.

0 replies

ben519 · 2021-10-24T16:52:19Z

ben519
Oct 24, 2021

I also have this question. Additionally..

Is there any benefit to including dependencies=[Depends(get_db_connection)] within the declaration of APIRouter(), considering we need to include it as a parameter in every path operation function? Seems unnecessarily redundant.

3 replies

juliocefe May 13, 2023

Same here

Version: fastapi[all]==0.95.1

Problem:
I am also stuck with this issue. I have declared Depends(get_db) in my router dependencies list, but I need to include the same Depends declaration in every route. Otherwise, FastAPI throws an error:
fastapi.exceptions.FastAPIError: Invalid args for response field! Hint: check that <class 'sqlalchemy.orm.session.Session'> is a valid Pydantic field type. more...

router = APIRouter(
    prefix="/users",
    dependencies=[Depends(get_db)],
)

# This declaration works
@router.get("/")
async def get_users(db: Session = Depends(get_db)) -> UserScheema:
    return crud.read_users(db)

# But, when I use this approach, FastAPI raises the aforementioned error.
@router.get("/")
async def get_users(db: Session) -> UserScheema:
    return crud.read_users(db)

Thank you for this amazing framework, I am loving the documentation ❤️.

juliocefe May 13, 2023

This solved my problem!
https://fastapi.tiangolo.com/tutorial/dependencies/#share-annotated-dependencies
Great!

will-e-yams Feb 9, 2024

Adding the Depends to the endpoint as a "fix" just proves the point of this bug.

marcodelmoral · 2022-12-06T15:35:56Z

marcodelmoral
Dec 6, 2022

Any ideas how to reduce redundancy in the declaration of router dependencies? I want to access my settings dependency, usually declared as a global dependency, inside my router endpoints.

0 replies

wesselvl1 · 2022-12-12T07:31:10Z

wesselvl1
Dec 12, 2022

router = APIRouter(
    prefix="/il_oedometer/casagrande",
    tags=["/il_oedometer/casagrande"],
    dependencies=[Depends(deps.get_casagrande_service)],
)

logger = logging.getLogger(__name__)
casagrandeService = deps.get_casagrande_service()

I actually did it like this so the casagrandeService is callable in all functions. But came here to figure out if this was a good way to tackle this or not. (Probably not)

1 reply

will-e-yams Feb 9, 2024

I don't see how this solves anything. Even without the router dependency casagrandeService would be available to any code below this.

will-e-yams · 2024-02-09T02:43:45Z

will-e-yams
Feb 9, 2024

I'm guessing no one figured this out and we have to put dependencies on each. and. every. endpoint.

Maybe I can convince someone to "Depend" all the routes and I can make it middleware.

2 replies

arielnmz Aug 3, 2024

Re:

I don't see how this solves anything.

I think the solution looks like this:

router = APIRouter(prefix="/items", tags=["items"])

DBSession = Annotated[Session, Depends(get_db)]

@router.get("/")
async def customers_list(db: DBSession) -> list[Item]:
    return db.do_something()

Two things:

Notice how I skipped dependencies=[Depends(get_db)] from APIRouter and instead declared annotated Session with the dep.
Notice how you don't have to do db: Session = Depends(get_db) on every route handler.

Imo seems counter intuitive, but I think the magic was that Session being Annotated makes FastAPI inject it to the route handler.

Answer selected by YuriiMotov

This comment was marked as off-topic.

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DJoepie · 2024-02-13T10:48:14Z

DJoepie
Feb 13, 2024

what is the point of dependencies=[Depends(some.dep)], if you can't actually use it on the endpoints?
For example, I need to pass my db as a dep on almost all routes in 1 router file but I can't seem to figure out how I can just transform
def read_user(user_id: int, db: Session = Depends(get_db)):
into
def read_user(user_id: int, db):

6 replies

DJoepie Feb 13, 2024

ohhh so if I understand you correctly I can protect all routes within the admin router with is_admin since I'm simply checking the authorization.

But if I want to do something with i.e. a database, I would still have to do that on a per route basis since I'm actively using the db "instance".

Do I understand what you're saying correctly like this?

will-e-yams Feb 14, 2024

Afaik, you are correct. But damn, I wish that we could inject dependencies at the router level.

Say I have admin router and I want to perform additional scrutiny:

Currently:

Add dependency to the router which keeps them out
Add a dependency to the endpoint that gives me access to the exact same data (to know who they are)

It's not the end of the world, but it is more boilerplate (and probably compute)

n8sty Feb 14, 2024

@DJoepie Yep, you're understanding correctly.

nfnfgo Sep 13, 2024

Router-level dependencies is limited in their functionality if we have no way to access the return value of the deps especially when we need to react based on the result of those dependencies 😭

fkapsahili Nov 6, 2024

Would a PR be reviewed for this? 🙂

mammothrider · 2025-06-13T03:01:41Z

mammothrider
Jun 13, 2025

edit: fix format

maybe adding a dict_dependencies and pass that as a default param to endpoints.

for example:

router = APIRouter(
    prefix="/project",
    tags=["project"],
    dict_dependencies=dict(
        conn = Depends(get_db_connection)
    ),
    responses={418: {"description": "Project status API."}},
)


@router.get("/count/{status}")
def projects_count(
    status: str, conn: pymssql.Connection # <- should get dep injection
) -> dict:
    try:
        if status.upper() == "ALL":
            status = None
        return aq.get_project_count(conn, status=status)
    except:
        raise HTTPException(404, "Unable to get project count")

2 replies

will-e-yams Jun 13, 2025

plz use triple backticks for code blocks, per markdown standards. single backticks are for code contained in a sentence.

that said, what is aq in this sample? (note the use of single backtick here)

ah, i see that you carried that over from the OP's question. i'm going to assume is a module for DB access that supports get_project_count.

A/ does this actually work?
B/ does it integrate with the OpenAPI docs?

this is what the docs say now, which while not a router dependency injection, is, at least, a bit more reusable:

https://fastapi.tiangolo.com/tutorial/dependencies/#create-a-dependency-or-dependable

from typing import Annotated

from fastapi import Depends, FastAPI

app = FastAPI()


async def common_parameters(q: str | None = None, skip: int = 0, limit: int = 100):
    return {"q": q, "skip": skip, "limit": limit}


@app.get("/items/")
async def read_items(commons: Annotated[dict, Depends(common_parameters)]):
    return commons


@app.get("/users/")
async def read_users(commons: Annotated[dict, Depends(common_parameters)]):
    return commons

being repurposed into injecting a local db connection as a parameter rather than query string params.

THIS IS AN UNTESTED APPROACH.

mammothrider Jun 18, 2025

plz use triple backticks for code blocks, per markdown standards. single backticks are for code contained in a sentence.

that said, what is aq in this sample? (note the use of single backtick here)

ah, i see that you carried that over from the OP's question. i'm going to assume is a module for DB access that supports get_project_count.

A/ does this actually work? B/ does it integrate with the OpenAPI docs?

this is what the docs say now, which while not a router dependency injection, is, at least, a bit more reusable:

https://fastapi.tiangolo.com/tutorial/dependencies/#create-a-dependency-or-dependable
from typing import Annotated

from fastapi import Depends, FastAPI

app = FastAPI()


async def common_parameters(q: str | None = None, skip: int = 0, limit: int = 100):
    return {"q": q, "skip": skip, "limit": limit}


@app.get("/items/")
async def read_items(commons: Annotated[dict, Depends(common_parameters)]):
    return commons


@app.get("/users/")
async def read_users(commons: Annotated[dict, Depends(common_parameters)]):
    return commons
being repurposed into injecting a local db connection as a parameter rather than query string params.

THIS IS AN UNTESTED APPROACH.

sry, format fixed.

for me, what the router dependencies can only do, is user verification. and for many endpoints under this router, there are some common dependecies, eg, get sql session.
Currently, I need to add a sql depends in every endpoint, and I think this could be add to router level.

PS:
I'm also consider directly getting the data in depends and doing verify, instead of getting sql session. And I'm still not sure if this is a good practice.

Uh oh!

How to use the router level dependency in the routes? #8810

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Example Code

Description

Operating System

Operating System Details

FastAPI Version

Python Version

Additional Context

Replies: 7 comments · 14 replies

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Replies: 7 comments 14 replies